1. Field of the Invention
The present invention relates to golf balls. Specifically, the present invention relates to improvement of dimples of golf balls.
2. Description of the Related Art
Golf balls have a large number of dimples on the surface thereof. The dimples disturb the air flow around the golf ball during flight to cause turbulent flow separation. By causing the turbulent flow separation, separation points of the air from the golf ball shift backwards. The turbulent flow separation promotes the displacement between the separation point on the upper side and the separation point on the lower side of the golf ball which results from the backspin.
A drag coefficient CD and a lift coefficient CL influence a trajectory of a golf ball. The United States Golf Association (USGA) has released a manual for a trajectory calculation program. By inputting a drag coefficient CD and a lift coefficient CL to a program that complies with the manual, a flight distance of a golf ball can be predicted. The drag coefficient CD and the lift coefficient CL are measured through the ITR (Indoor Test Range) specified in the rule of the USGA.
US2007/0093319 discloses a golf ball in which a lift force falls within a predetermined range at a Reynolds Number of 205000 and a spin rate of 2900 rpm.
US2007/0093320 discloses a golf ball in which a drag coefficient CD and a lift coefficient CL fall within predetermined ranges at a Reynolds Number of 230000 and a spin ratio of 0.085.
The drag coefficient CD and the lift coefficient CL change moment by moment from a launch point to a landing point. In the golf ball disclosed in US2007/0093319, the lift force at one time point in a trajectory is merely set within the predetermined range. Evaluation regarding the flight performance of the golf ball is not sufficient. In the golf ball disclosed in US2007/0093320, the drag coefficient CD and the lift coefficient CL at one time point in a trajectory are merely set within the predetermined ranges. Evaluation regarding the flight performance of the golf ball is also not sufficient.
An object of the present invention is to provide a golf ball having excellent flight performance.